1. Field of the Invention
The invention relates to a method and apparatus for erecting a bridge structure and a bridge structure suitable for use above a body of water, wherein the bridge structure is connected to an existing structure and a gas flare line and gas flare tip is associated with the bridge structure. The gas flare line and gas flare tip is utilized for burning, or flaring, excess natural gas produced at an offshore oil well platform.
2. Description of the Prior Art
In offshore oil drilling and/or producing operations, excess amounts of natural gas are produced as a result of these operations. Frequently, this excess gas is disposed of by flaring, or burning it. For safety reasons, the flaring operation must be conducted at a remote location from the offshore platform, since the resultant heat given off by the flaring operation could cause a fire hazard and/or damage the offshore platform and its personnel.
Accordingly, many different apparatus have been proposed to enable the flaring operation to be conducted at a location remote from the platform. One type of apparatus utilized in conjunction with offshore platforms for flaring excess gas is exemplified in U.S. Pat. No. 2,894,269, issued July 14, 1959, to R. J. Dodge; U.S. Pat. No. 3,666,395, issued May 30, 1972, to J. W. Kubasta; and U.S. Pat. No. 3,902,843, issued Sept. 2, 1975, to M. Genini et al. This type of apparatus utilizes a submerged pipeline for transporting the gas from the offshore platform to a flare structure which is anchored to the underwater surface. The gas flare apparatus in the foregoing patents has some type of flexible connection between the gas flare and the lowermost portion of the device in contact with the underwater surface, whereby the gas flare is subject to movement caused by wave action and ocean currents.
Many problems are encountered in using the foregoing type of apparatus in deep-water offshore installations. Since the pipeline is submerged, there are many inherent problems relating to maintenance and construction of that pipeline. For example, were the pipeline to develop any leaks, the use of divers would be necessary to repair the pipeline. Accordingly, the cost of such repairs could be quite expensive, in addition to the difficulty in initially determining whether or not the submerged pipeline has any leaks. Furthermore, a submerged pipeline is subjected to excessive forces caused by water pressure, wave action, and/or ocean currents, whereby the pipeline must be constructed to withstand such forces. Such construction may substantially increase the cost of the flare installation. Furthermore, since the gas flare apparatus is capable of movement, the pipeline may be subjected to tensional forces as the gas flare moves away from the offshore platform, thus pulling the pipeline outwardly from the platform. This problem is believed to be particularly troublesome with respect to the apparatus of the Kubasta patent and could readily cause damage to the submerged pipeline.
Another approach has been suggested wherein a gas flare line and glas flare tip is supported from a cantilevered structure attached to the offshore platform. An example of this approach is found in U.S. Pat. No. 3,807,932, issued Apr. 30, 1974, to J. J. Dewald. The structure disclosed in this patent is utilized to support an apparatus for burning, or flaring, excess oil produced in the course of drilling and/or testing offshore oil wells. The disadvantages of this approach are numerous.
If a large volume of excess gas is to be flared, the heat generated by the flaring operation requires that the flare tip be disposed quite a great distance from the offshore platform in order to avoid damage to the platform and/or personnel working thereon. Some installations presently in use require the flare tip to be located approximately 400 feet from the offshore platform. As is readily apparent, the construction of a cantilevered support for a gas flare line and gas flare tip having such a great length presents many problems. In addition to the great expense involved, constructing such a support under potentially adverse weather conditions prevalent at deep-water offshore locations could present many problems in installing such a cantilever support. For example, the patent of Dewald suggests that the cantilevered support is swung into place by a crane, or similar device, whereupon the cantilevered support is then aligned with a support disposed on the offshore platform and the cantilevered support is then pinned to the offshore platform. Such a procedure would be extremely difficult when attempting to mount a cantilevered support with a length approximating 400 feet, since aligning the cantilevered support such that it could be pinned to the offshore platform would be extremely difficult under the weather conditions prevalent at many deep-water offshore platform locations. For example, were the cantilevered support to be lifted by a crane disposed upon the offshore platform, great difficulty and expense would be encountered in attempting to align the cantilevered support with its mounting bracket disposed on the offshore platform due to the fact that the center of gravity of the cantilevered support would be located approximately 200 feet from the offshore platform. In order to adequately balance the cantilevered support such that the support would not tilt toward the ocean, the boom of a crane located upon the offshore platform would have to have a length in excess of 200 feet. If the crane were to be disposed upon a barge located at a location remote from the offshore platform, the crane would be subject to the slightest movement caused by wave or wind action upon the barge, whereby it would be extremely difficult to align the cantilevered support to its mounting brackets disposed upon the offshore platform.
Another problem which could result when utilizing a cantilevered support for the gas flare line and gas flare tip could result from the fact that all the forces exerted upon the cantilevered support are borne by its mounting bracket disposed on the offshore platform. High wind and heavy sea conditions acting upon the end of a cantilevered support of a substantial length could result in the mounting bracket being torn loose from the offshore platform, since the end of the cantilevered support, which is remotely disposed from the offshore platform, does not have any support beneath it for providing additional stabilization to the cantilevered support.
Accordingly, prior to the development of the present invention, there has been no method and apparatus for erecting a bridge structure suitable for use above a body of water which is economical to use and erect, easily erected in deep-water offshore locations, and can withstand the adverse weather conditions prevalent in such locations. Therefore, the art has sought a method and apparatus for erecting a bridge structure and a bridge structure suitable for use above a body of water which provides an easily erected, economical bridge structure capable of being erected at a deep-water offshore locations and withstanding the potentially adverse weather conditions prevalent at such locations, absent the problems of previously proposed bridge structures.